The pre-treatment of cattle feed or roughage, before feeding it to cattle, has long been a subject of research. For instance, during the drought years of the 1930's, there was a need to make cattle feed out of weeds and about anything else that was growing. It was then demonstrated that almost any organic material having any potential as fodder could be made into digestible animal feed. The green fodder could be preserved and converted into animal feed within a silo or similar storage. The process of storing and preserving fodder is known as ensiling.
Ensilage is essentially a partially fermented organic material. Most temperate regions of the planet generate large amounts of organic material, commonly called biomass. Most biomass is considered a waste material and typically disposed of as rubbish. Much of this waste material could be converted into a plant growth media and methane (CH.sub.4) by first converting it to silage and then processing it through an anaerobic methane producing digester.
The anaerobic digestion process can be fed by an enormous variety of biomass sources. As a result, the process can be used to resolve an equally wide variety of waste disposal problems. If this waste biomass can be efficiently converted into energy, it could be utilized to replace scarce fossil fuels.
Some site specific sources of biomass include:
Dairy farms Fruit processors Mint farms Cheese plants Potato processors Hog farms Cattle feed lots Egg farms Poultry farms Hop farms Frozen food processors
Some examples of particular biomass materials include:
 Wheat straw Corn silage Rice Straw Food wastes Grass seed straw Residential yard Selected municipal debris solid wastes
The physical aspects of an anaerobic digester system are essentially a vessel and all of the necessary accessories and other components to create an environment as close as possible to that in which the anaerobe microorganisms naturally live. The initial digestive chambers of bovines are excellent examples of a well functioning anaerobic digester found in nature. The ingestion of grasses or other similar materials by the bovine ultimately produces a manure mash, which is an excellent fertilizer, and produces a methane gas (CH.sub.4) emission, as a by-product.
Operating an efficient anaerobic digester roughly patterned after naturally occurring digestive systems, but at an industrial scale, is not a simple task. The feedstocks for such industrial processes are substantially composed of biologically generated material.
A lack of uniform quality of the end product is almost universal in most, if not all, existing industrial scaled anaerobic digesters, and composting operations of a significant scale. This lack in uniformity has led to the dismissal of anaerobic digestion as a viable, reliable methane industrial scale source of methane. To operate even a simple anaerobic digester that substantially mimics the biomass digestive systems found in nature, powerful and sensitive system monitoring methods and controls are needed. This is because in the natural bovine system, hundreds of thousands or even millions of minute and symbiotic organisms have evolved over eons to a self-regulating system.
In the industrial setting, we can observe an example of a high level of sensitivity in the precision of an industrial fermentation process, as typically performed to produce a top quality beer. Typical industrial process control systems use at least one physical parameter, such as pressure, time or temperature for a primary control. When closer control is needed, a second physical parameter is used. Occasionally, a third parameter may also be employed. The use of this "third" parameter or 3.sup.rd level of control usually results in a process control system with much higher precision than that process's ability to be accurately controlled.
Currently, in most industrial scale anaerobic digesters, the design of various components of the digesters coupled with the control system together allow the temperature to fluctuate anywhere from plus or minus two or three degrees Fahrenheit (F.), up to occasional variations having a range often degrees F., or more. For the digester's anaerobes, even a single degree F change in temperature is at least one hundred times greater than the phenomena that needs to be measured, which is the heat generated by the anaerobes. Therefore, for these conventional industrial digesters, the ten degree "dead band" or noise level of the signal from the phenomena to be measured or controlled, is ten to one hundred times larger than the phenomena's metabolic heat signal that needs to be accurately measured.
A precision control system is of no benefit for these conventional, industrial anaerobic digester systems, because the physical design of the anaerobic digester does not permit "fine tuning" due to the errors produced by the measurement and control system. Therefore, a need exists for both a digester design and a control system for an industrial anaerobic digester, which are better able to monitor and control the anaerobic process.